1. Field of the Invention
The present invention is broadly concerned with improved anti-corrosion coating systems especially designed for use in the oil and gas industry for treatment of downhole oil and gas well metallic surfaces. More particularly, the invention pertains to such coating systems made up of an epoxy and a curing agent, the latter being selected from the group consisting of the alkoxylated amines and the imidazolines and mixtures thereof. The coating systems of the invention are resistant to freezing and do not suffer from the tendency to agglomerate or "clabber" in the presence of downhole formation water containing significant quantities of chloride ion and sulfur compounds.
2. Description of the Prior Art
It is well known that oil and gas wells are subject to extensive corrosion. Downhole equipment such as sucker rods, pump rods, tubing and casing are generally made of mild steel which is adversely affected by the production fluid of the well. The often high temperatures and acidic nature of the production fluids and formation waters magnifies these corrosion problems.
A variety of anti-corrosion systems have been described in the past. Many corrosion inhibitors are aqueous dispersions containing a variety of components, e.g., 2-mercaptobenzothiozole, benzotriozole, tolyltriozole, phosphates, polyphosphates, organic soluble polymers, silicates, dithiocarbamates, nitrites, oxazoles, imidazoles, imidazolines, lignands, lignosulfates, tannins, phosphoric acid esters and boric acid esters. Many of these inhibitors are very prone to freezing during cold weather, making them very difficult to handle and maintain. Moreover, the useful life of many prior anti-corrosion treatments is very short, e.g., a week or less.
U.S. Pat. No. 4,526,813 describes composite systems made up of an epoxy resin, an alcohol and an amine curing agent such as N-tallow-1,3-diaminopropane. The tallow diamine curing agent in aromatic solvent has a tendency to freeze in cold weather conditions, necessitating the presence of the alcohol. In addition, the alcohol tends to inhibit agglomeration or clabbering which materially detracts from the utility of the anti-corrosion film.